Segmented development electrode



March 12, 1957 H. E. CRUMRINE ETAL 2,784,694

SEGMENTED DEVELOPMENT ELECTRODE Filed Feb. 8, 1955 I4 I i' ENTlAL I3CHARGING AREA 15 SOURCE (I EXPOSURE STATIONQO) TRANSFER AREA (24)DEVELOPING AREA (2!) BRUSH CONTROL MECHANISM MAGNETIC 3| ACTUATORMAGNETIC '32 ACTUATOR \SEQLENTIAL MAGNETIC 6 ACTUATOR MAGNETIC34-ACTUATOR MAGNETIC 35 ACTUATOR INVENTOR HERBERT Ev CRUMRINE .CLYDE R.MAYO ATTORNEYS United States Patent I 2,784,694 SEGMENTED DEVELOPMENTELECTRODE Herbert E. Crumrine and Clyde R. Mayo, Rochester, N. Y.,assignors to The Haloid Company, Rochester, N. Y., a corporation of NewYork Application February 8, 1955, Serial No. 486,763

9 Claims. (Cl. 118--51) The present invention relates to xerographictechniques, and more particularly to a segmented development electrodefor incorporation in apparatus adapted to develop a powder image on theinsulating image layer of a xerographic plate.

In the production of xerographic copies, the photoconductive insulatingimage layer of the xerographic plate is first charged electrostatically,the charged surface then being exposed under light to the subject to becopied, thereby forming an electrostatic image. Thereafter the imagelayer having the electrostatic image thereon is subjected to a cloud ofelectroscopic or developer powder to produce a powder image, which isthen transferred and afiixed to paper or other transfer medium.

In the making of powder images on insulating layers that have beencharged electrostatically, it has been found that undesirable effectsarise in the background :areas due to the adherence of portions of theelectroscopic powder to the non-image areas of the plate on which theimage layer is supported. The powder that adheres to the non-image areasis carried on to the transfer sheet :along with the powder on the imageareas. Such powder :as remains on the non-image areas is subsequentlycharged :and causes a build-up of powder and a continual increasing ofundesirable effects in the background areas in printing operation.

The present invention has particular reference to techniques involvingthe use of developing materials consisting of a combination of finelydivided pigmented electroscopic powder with a coarser carrier material.The carrier material is triboelectrically charged with a polar iityopposite to that of the electroscopic powder upon frictional engagementtherewith and acts to retain the elect-roscopic powder which isattracted to and surrounds the particles of carrier material. If thecharge on the nonimage areas of the plate has a greater attractive forcefor the electroscopic powder particles than has the charge on thecarrier material, the electroscopic powder particles are likely. to beattracted to and held by the non-image areas on the plate, even thoughsuch non-image areas are of a conductive character, to drain off themajor part of the electrostatic charge except over the insulating image:areas.

It has hitherto been suggested to impose a further electrostatic chargeon the non-image areas of the plate or to surround said areas with anelectrostatic field such that the charge on the non-image areas willhave a polarity opposing the charge on the image areas and the same asthat on the electroscopic powder. Thus, the charge on the non-imageareas will repel the electroscopic powder and prevent its adherence tothe non-image areas. For this purpose a charged development electrodehas been incorporated in continuous printing machines or in othermechanismsfor applying electroscopic powder to a charged image layer,whereby the powder will be applied evenly and: uniformly over the'imageareas of the plate andthenon-image areas will be left substantially freeof electroscopic powder.

.ice

In line copy work employing a cascade type of de; velopment, thedevelopment electrode serves to clear up the white background in thecopy. When xerography is used for continuous tone reproductions, thedevelopment electrode then serves the significant purpose of improvingthe tone relationship between the copy and the original. In either case,the development electrode makes possible the reproduction of solid blackareas.

For example, in the Patent No. 2,573,881 issued to Walkup et al., adevelopment electrode is disclosed operating in conjunction with arotary mechanism. Similarly, in the co-pending application of Hayfordand Crumrine, S. N. 456,538, filed September 16, 1954 entitledXerographic Development Electrode, there is disclosed a developmentelectrode incorporated in a continuous and automatic xerographic device.

During development of the electrostatic latent image on thephotoconductive insulating surface, fine powder particles are broughtinto the field of influence of the charges on the surface and aredeposited on charged areas. The development electrode, which is spacedat a slight distance from this sensitive layer, tends to build-up on itssurface a coating of developer material. As long as this powderaccumulation remains light, the image which is developed is ordinarilynot affected adversely. However, a relatively heavy coating of developermaterial on the development electrode interposes a new surface betweenthe sensitive layer and the development electrode. If the coatingparticles carry an electrostatic charge, this may effectively alter thebias potential on the electrode and substantially diminish thebeneficial aspects of the development electrode during development ofthe electrostatic image.

This coating also introduces uncontrollable factors in the developmentprocess. Such lack of control is to some extent attributable to the factthat the powder coating forming on the developer electrode is generallyuneven and assumes random patterns. A heavy coating may dropagglomerates of developer powder to the plate surface, glVlIlg rise to anon-uniform, distorted development of the electrostatic image pattern.Moreover, a heavy coating may result in the presentation of irregularand uncontrolled flow patterns of the developer material to the platesurface and will cause streaking of the developed image.

In the above-identified co-pending application it is proposed to limitthe deposition of powder on the developgraphic plate for cleaning thepowder deposition from While such apparatus serves to limit the Suchenlargehere there are as in aircraft installations. ipal object of thepresent d means and methods to ment is highly undesirable, particularlyw severe limitations as to space,

Accordingly, it is the princ invention to provide improve remaindeposited on the developement electrode.

More particularly, it is an object of the invention to provide acleanable development electrode for a rotary drum-xerographie plate,which electrode has a width not exceeding that of theplate. v

It is another object of the invention to provide a development electrodefor a continuously operating xerographic apparatus, which developmentelectrode is constituted by an array of segments. I Meansare alsoprovided for reversing the position of the segments relative to theassociated xerogra'phic plate to permit the cleaning thereof, 7

' Briefly stated, the invention embodies a segmented electrode whereineach segment is pivotally mounted and coupled to a mechanism adapted toreverse the position thereof relative to the associated xerographicplate, the segments being preferably reversed sequentially to minimizedisruption of the electrostatic field. Brushing means are adaptedtotravel over the reversed face of the segments and to clean off thepowder deposition thereon. I

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the following detaileddescription of the invention to be read in connection with theaccompanying drawing, wherein like elements are identified by likereference numerals.

' In the drawing:

Fig. 1 illustrates schematically a preferred embodiment of anelectrophotographic apparatus adapted, for continuous and automaticoperation, and incorporating a segmented development electrode inaccordance with the invention.

Fig. 2 is an enlarged side view of the segmented electrode inconjunction with the actuating mechanism therefor. 7

Referring now to the drawing, the continuously operating xerographicapparatus shown in Fig. 1 comprises a xerographic plate formed in theshape of a rotating drum, generally designated by numeral 14 andcomposed of a conductive backing member 11 and a photoconductiveinsulating layer 12. Conductive backing member 11 is held at a groundpotential.

A uniform electrostatic charge is imposed on layer 12 by a coronadischarge electrode 13, which is connected to a high-voltage source 1-The charge is impressed on layer 12 in the region thereof designated inthe drawing by numeral 15. An image. 16 on a surface moving at aproperlinear speed is illuminated by lamps 17 and is projected through slit 19and lens 18 at an exposure station, generally designated by numeral 20,whereby anelectrostatic latent image is formed on sensitive layer 12.

At an angular position relative to drum 11, designated by numeral 21,the development of the electrostatic latent image takes place. Asuitable developer cloud supply 22 feeds a cloud of developerparticles-suspended in air to the space defined between layer 12 and asegmented development electrode 23, which electrode will be described ingreater detail in connection with Fig. 2. At the area generallydesignated by numeral 24, transfer of the developed image from layer 12occurs.- A roller 25 supplies a continuously fed web 26 under roller 27and into contact with layer 12, whereby an adhesive form of transfer iseffected, web 26 having an adhesive coating on one surface thereof andbeing subjected'to pressure by roller 27.

The web is then fed, carrying the transferred image, through an imagefusing apparatus 28, wherein the copy is made permanent, and finally onto roller 29. The movement of web 26 is synchronized with the turning ofdrum 10, which in this embodiment is rotated in the clockwise direction,as indicated by the arrow. The drum and the web 26 may be driven by asuitable motor (not shown) or by other conventional means. In addition,a cleaning device (not shown) may be positioned along the path ofrotation of the xerographic plate subsequent to the transfer area toclean the plate surface prior to charging or sensitizing.

Referring now to Fig. 2, it will be seen that the segmented developmentelectrode 23 is generally arcuatein form and conforms to the curvatureof the drum. The width of this electrode substantially corresponds tothat of the rotating drum. The segmented electrode 23 is constituted bya plurality of closely spaced, rectangular slats or segments 23A23F, theindividual segments being small to bring about proper curvature and evenspacing of the development electrode. Segments 23A23F are pivotallymounted at their upper ends on suitable shafts 23a-23f, whereby a halfrevolution of a shaft in the counter-clockwise direction turns over therelated segment to present the reverse face thereof to the xerographicplate 12. As indicated by the dashed line with respect to segment 23A,the segment when reversed is shifted upwardly in position, therebyleaving a gap in the electrode which may thereafter be occupied by theadjacent segment when reversed. Thus, when all the segments are reversedthe development electrode is effectively shifted upwardly along the drumto an extent equal to the size of one segment.

To prevent the shift of the development electrode upon reversal of thesegments thereof, an extra segment may be provided at each end of theelectrode. The extra electrode may be adapted to move only to fill inthe opening as the adjacent plates are reversed, thereby pre-' ventingthe effective movement of the electrode.

The electrode segments are electrically interconnected and coupled to asuitable bias source to establish an electrostatic field in the areabetween the electrode and the xerographic plate. It will be evident thateither face of the electrode segments is operative to establish thedesired field;

The spacing of the segmented development electrode with respect to thexerographic plate is quite close and it is necessary to carry outcleaning of theelectrode continuously during the operation of themechanism. The electrode is cleaned by turning over the segments thereofsequentially to bring the dirty surface of the electrode upward and awayfrom the plate and a clean surface to the plate. The dirty surfaces ofthe electrode segments are then swept clean by means such as a rotarybrush 38 and turned back to face the plate.

In order to effect the sequential turning over of the segments, theshaft of each segment is coupled to a suitable actuating mechanism, suchas electromagnetic actuators 30-35 coupled to shafts 23'a23f,respectively. Each actuator, which may include a conventional solenoidand armature, is designed so that when energized it acts instantly toreverse the position of the associated segment, and when de-energized itfunctions to restore the segment to its initial position. For thepurpose of energizing or tie-energizing the actuators in the desiredmanner, a sequential timer 36 is provided which supplies opcratingvoltages successively to the actuators. In its simplest form the timermay consist of a motor-driven rotary multi-contact switch coupled to apower source and having a moving contact arranged to connect said sourcecyclically and sequentially to the actuators, such that each segment isactuated in turn until all are reversed and after a predetermined periodall of the actuators are simultaneously released to cause said segmentsto revert to their original position. The cycle is then repeated. Therotary brush 24 is arranged to travel along the dirty outer surface. Theoperation of the brush is controlled by a suitable control mechanism 37synchronized bytimer 36 so that after all the segments are reversed, thebrush sweeps down the electrode to remove the powder, while after thesegments return to their original position, the brush sweeps'up theelectrode. Thus, both faces of the electrode are kept clean.

The mechanism for eife'ctingth'e desired movement of the brush may besimilar to" that disclosed in theco on the surface facing theXerographic plate. The invention is by no means limited ot rotarybrushes for cleaning purposes, and in lieu thereof moving felt pads orsimilar means may be successfully employed.

To prevent excessive loss of powder cloud when the segment is reversed,it is desirable that the reversal be carried out as quickly as possible.Accordingly, the actuators should be of the fast-acting type. It is tobe understood that the invention is not limited to magnetic actuationand that the reversal of the segment may be carried out by various othermechanisms, such as those used to operate louvres. It is also possibleto reverse the position of the several segments concurrently, ratherthan sequentially.

While there has been described what at present is considered to be apreferred embodiment of the invention, it is to be understood that manychanges and modifications may be made therein without departing from theessential spirit of the invention. It is intended therefore in theappended claims to cover all such modifications as fall within the truescope of the invention.

What is claimed is:

1. In a xerographic apparatus, the combination comprising a Xerographicplate, a development electrode in closely spaced relation to said plate,said electrode being constituted by a plurality of reversible segments,and means for reversibly positioning said segments relative to theplate, whereby either surface of the electrode may be presented inface-to-face relation to said plate.

2. In a Xerographic apparatus, the combination com prising a cylindricalxerographic plate, a generally arcuate development electrode disposed inparallel spaced relation to said plate, said electrode being constitutedby an array of rectangular segments whose width correspondssubstantially to that of said plate, said segments being pivotallymounted whereby either surface thereof may be presented to said plate byreversal of said segments, and means for reversibly positioning saidsegments relative to the plate.

3. In a xerographic apparatus, the combination comprising a xerographicplate, a development electrode in closely spaced relation to said plate,said electrode being constituted by a plurality of reversible segments,means for reversibly positioning said segments relative to the plate,whereby either surface of the electrode may be presented in face-to-facerelation to said plate, and cleaning means for removing depositedmaterial from the surface of said electrode turned away from said plate.

4. In a Xerographic apparatus, the combination comprising a cylindricalXerographic plate, a generally arcuate development electrode disposed inparallel spaced relation to said plate, said electrode being constitutedby an array of rectangular segments whose width correspondssubstantially to that of said plate, said segments being pivotallymounted whereby either surface thereof may be presented to said plate byreversal of said segments, means for reversibly positioning saidsegments relative to the plate, means to spray a gas suspension ofpowder into the space between said plate and said electrode, andcleaning means for removing deposited material from the surface of saidelectrode turned away from said plate.

5. In a Xerographic apparatus, the combination comprising a cylindricalxerographic plate, a generally arouate development electrode disposed inparallel spaced relation to said plate, said electrode being constitutedby an array of rectangular segments whose width correspondssubstantially to that of said plate, said segments being pivotallymounted whereby either surface thereof may be presented to said plate byreversal of said segments, means to spray a powder cloud in the spacebetween said plate and said electrode, actuating means operablesequentially for reversibly positioning the segments relative to theplate successively, and means for removing deposited powder from thesurface of said electrode turned away from said plate.

6. Xerographic apparatus comprising a Xerographic plate, a segmenteddevelopment electrode, disposed in spaced parallel relation to saidplate and constituted by an array of conductive segments, each segmentbeing pivotally mounted on a shaft, an actuator coupled to each shaft,means for sequentially energizing said actuators for reversiblypositioning said segments relative to the plate successively, and meansto feed a powder cloud in the space between said electrode and saidplate.

7. Xerographic apparatus comprising a xerographic plate, a segmenteddevelopment electrode disposed in spaced parallel relation to said plateand constituted by an array of conductive segments, each segment beingpivotally mounted on a shaft, an actuator coupled to each shaft, meansfor sequentially energizing said actuators for reversibly positioningsaid segments relative to the plate successively, means to feed a powdercloud in the space between said electrode and said plate, and brushmeans arranged to travel across said electrode on the surface thereofturned away from said plate to remove powder deposit therefrom, saidbrush means being operative upon completion of said sequence.

8. Apparatus as set forth in claim 7, wherein said sequential energizingmeans is constituted by a timing device to effect cyclical andsequential reversal of said segments.

9. Apparatus as set forth in claim 8, wherein said brush means isoperated by a control mechanism synchronized by said timer periodicallyto clean the turned away surface of said electrode.

References Cited in the file of this patent UNITED STATES PATENTS1,869,772 Paterniti Aug. 2, 1932 2,254,135 Boer Aug. 26, 1941 2,383,112Dahlman Aug. 21, 1945 2,551,582 Carlson May 8, 1951 2,573,881 Walkup etal Nov. 6, 1.951 2,625,238 Roper Jan. 13, 1953 2,691,345 Huebner Oct.12, 1954

